1. Relevant Field
The invention relates to the field of position determination. In particular, the field relates to using light information to aid in position determination.
2. Relevant Background
In order for a mobile device to determine its position, a receiver may need to acquire the signals from one or more satellite vehicles (SV). The initial acquisition of each SV signal can be computationally intensive and may take up to several minutes. These position location operations can be particularly demanding upon system performance; for example an attempted location fix may consume several seconds or more, during which time the mobile device's communication functionality may be diminished. Therefore, it is often valuable for a mobile device to understand the environment in which it is located before searching for satellite positioning systems (SPS) or terrestrial signals.
A mobile device can save power and make better use of its processing power if, for example, a mobile device can be characterized to be indoors, then it may be reasonable to assume that the mobile device is either static or moving at pedestrian speeds. Furthermore, if the mobile device is indoors, it may be reasonable to assume a certain amount of blockage between the mobile device and the open sky, causing SPS signals to be weaker when received at the mobile device. The weak SPS signals may call for searching for signals with greater sensitivity, so that extra processing power can be used to integrate the weak signals to the point where they can be used to provide positioning or timing information. Alternatively, it may be useful to search for stronger, terrestrial signals first, to determine if sufficient accuracy can be provided without having to search longer for SPS signals.
If, for example, a mobile device can be determined to be outdoors, then it may be reasonable to assume less and/or no blockage between the mobile device and the open sky, producing SPS signals to be stronger when received at the mobile device. The strong SPS signals may call for searching for signals more broadly and/or with lesser sensitivity, allowing the extra processing power to be used in other applications.
Therefore, there is a need for a mobile device to understand the environment in which it is located before searching for SPS signals or terrestrial signals.